High throughput cell-based phenotypic screening becomes necessary to take advantage of the wealth of data obtained from systematic genome sequencing. Genome wide gene silencing by siRNA is now possible on cultured cells. Alternatively, one would like to rapidly identify biologically active compounds from drugs libraries able to enhance or inhibit specific cell functions. The aim is thus to carry out phenotypic analyses on cultured cells with an automated tool.
High throughput methods have long been used to perform quantitative dosages on known molecular pathways. These methods cannot be used when one wants to identify new genes involved in complex cell properties like protein transport, adhesion, migration, division or apoptosis, or to probe the ability of a new drug to interfere with those mechanisms.
The challenge nowadays is to associate the accuracy of modern cell biology analysis on a small number of cells to the power of high throughput automated methods on a great number of cells. Answers to this challenge are not numerous because of several barriers:                First, the cell population on the bottom of wells has a distribution which cannot be predicted. This imposes the use of small magnification objectives or an automated but lengthy scanning acquisition.        Second, the cell shape is different from one cell to another and this parameter cannot be ignored whatever the phenotype under analysis or the quantification performed on a cell basis (intracellular localisation, number and size of particular organelles, molecular signals.).        Third, the intracellular distribution of cell compartments and the global cell organisation are also varying considerably from one cell to another. This is particularly cumbersome. It prevents any kind of precise analysis of the mutual distribution of intracellular compartments, or of the establishment and maintenance of cell polarity during cell division or cell migration.        The distribution of the cell population as well as the shape and internal organisation of individual cells, are all dependent on cell migration activity. Motility can vary largely depending on the cell type, but it is always a significant parameter.        
Overcoming these difficulties would require a method to prevent cells from migrating and to orientate every cell in the same way with respect to an external clue. An answer has been provided with the micro-patterning which allows a precise control of cell shape and cell position by influencing actin assembly. Many possibilities of the micro-patterning have been investigated (Whitesides and Ingber; U.S. Pat. No. 6,368,838; WO 01/70389; WO 02/86452; WO 02/22787) but none of them influence the entire functional and structural polarity in a repetitive way compatible with a precise screening of cell intrinsic properties.